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Metallothioneins are low-molecular-weight, Cys-rich proteins that are ubiquitous in eukaryotic organisms. Since their first description as cadmium-and zinc-binding proteins in horse kidneys, metallothionein genes and proteins have been characterized from many different organisms (reviewed by Hamer, 1986;Robinson et al., 1993). In the plant kingdom, a few metallothionein-like genes have been characterized recently, including those from peas (Evans et al., 1990), maize (De Framond, 1991), Arabidopsis (Zhou and Goldsbrough, 1994, 1995), and Sambucus nigra (Coupe et al., 1995).Because of the nature of its metal-binding activity and induction by heavy metal ions, metallothionein is strongly believed to have a role in metal metabolism or detoxification (Hamer, 1986). However, some plant metallothioneinlike genes are not stimulated by heavy metal (De Miranda et al., 1990;Kawashima et al., 1992). In recent studies with cloned Brassica and Sambucus metallothionein-like genes, the accumulation of their mRNAs in the senesced leaflet